The present invention relates to apparatuses and methods for wind turbines, and, more particularly to retrofitting wind turbines and new wind turbines having a variable speed auxiliary generator and an algorithm for load sharing with the main generator.
Older wind turbines are of the fixed speed and fixed pitch variety. Their efficiency is never optimized because wind speeds vary and wind input varies. Newer wind turbines (doubly fed turbines and fully converted turbines) are of the variable speed and variable pitch variety. They have a variable output from the gear box which creates a variable frequency and voltage from the generator. Then, in order to be coupled directly to the constant frequency and voltage of the electric grid, these wind turbines employ power electronics, i.e. a converter, (or in the case of a doubly fed turbine a partial converter) to convert the variable frequency and voltage of the generator to the constant frequency and voltage of the electric grid. However, this power electronics is (i) very expensive, (ii) of heavy weight, (iii) unreliable and (iv) creates additional losses.
Another problem is that wind turbines have become an increasing percentage of the turbines that connect to electric power grids and have therefore recently come to be more scrutinized for grid compliance. Grid compliance means being configured to be able to help a fallen grid come back up, minimizing reactive power and complying with low voltage ride through requirements.
Another important factor is keeping the cost of manufacturing to a minimum.
In order to maximize production of electrical output, wind turbines should be as efficient as possible. There is a compelling need to have an apparatus and method that will improve the reliability and energy efficiency of wind turbines while providing wind turbines at the exact conditions demanded by electric grids and at reasonable cost. It would be particularly helpful to be able to reap the benefits that the variable speed variable pitch wind turbines have over the fixed speed wind turbines without experiencing the disadvantages of the variable speed wind turbines, and yet to do so at a reasonable cost.